The present invention relates to a method of recording digital video and audio signals.
In comparison with a conventional analog recording type video tape recorder (hereinbelow, referred to as an "AVCR"), the reproduced image quality and reproduced sound quality are more excellent in a digital recording type video tape recorder (hereinbelow, referred to as a "DVCR") in which video and audio signals are recorded digitally. D1-format is one example of formats of DVCRs, a small number of which are put to practical use. As shown in FIG. 1, a D1-format tape has linear tracks on its opposite sides, such as an analog audio cue track AT for recording audio references, a control track CT for recording tracking control signals and a time code track TT for recording time codes and user's data. These linear tracks are provided for improving efficiency of editing.
Meanwhile, between the linear tracks, the D1-format tape has a plurality of helical tracks acting as signal tracks ST, respectively, two of which are illustrated in FIG. 1. Each signal track ST is constituted by two video bursts V for recording video signals, four audio bursts A interposed between the video bursts V, five gaps G among the video bursts V and the audio bursts A and two ambles B for interposing the video bursts V therebetween. Even and odd components of each audio channel are recorded on these four audio bursts A. Namely, in the case of 4-channel audio data, signal tracks 1 to 4 form one unit for recording 4-channel audio data and 4-channel audio data are recorded by repeating sequence of the signal tracks 1 to 4 as follows:
______________________________________ Track 1: Ch 1 - Even, Ch 4 - Odd, Ch 3 - Even, Ch 2 - Odd, Track 2: Ch 2 - Even, Ch 1 - Odd, Ch 4 - Even, Ch 3 - Odd, Track 3: Ch 3 - Even, Ch 2 - Odd, Ch 1 - Even, Ch 4 - Odd, Track 4: Ch 4 - Even, Ch 3 - Odd, Ch 2 - Even, Ch 1 - Odd. ______________________________________
In the above, "Ch" denotes a channel. D1-format is used for broadcasting and therefore, should have sufficiently high image and sound quality. Thus, luminance components and color difference components of video signals have sampling frequencies of 13.5 MHz and 6.75 MHz, respectively. Meanwhile, audio signals have a single sampling frequency of 48 kHz which is phase locked to the sampling frequencies of the video signals.
In VCRs for broadcasting use, it is essential to perform complete and independent editing. However, it is not guaranteed that a mechanical accuracy of 100% cannot be achieved even in VCRs for broadcasting use. Namely, for example, in the case where an already recorded audio burst is rewritten at the time of editing, it is impossible to record new signals at locations completely identical with those of the original audio burst.
Therefore, if a guard between neighboring signal tracks or the gaps are not provided, the audio bursts adjacent to the audio burst to be rewritten are disturbed by rewriting, thereby resulting in an increase of errors at the time of reproduction. In VCRs for broadcasting use, such deterioration in the quality of recording signals is not permitted. On the above mentioned ground, the gaps and the guards are set at sufficiently large values in order to prevent the deterioration in the quality of recorded data.
To this end, the D1-format tape has a width of 19 mm, a maximum length of 1,600 m (maximum recording time of 94 min.). Furthermore, a tape cassette for the D1-format tape is far larger than a commercially available tape cassette for a 1/2-inch tape of a maximum recording time of 480 min. However, in broadcasting, greater importance is attached to editing performance than the large size of the tape cassette and the short recording time. In other words, in order to improve editing performance of the D1-format tape, additional areas which are not used for recording, such as the gaps and the guards are required to be provided even at the sacrifice of the recording time.
On the other hand, in order to put DVCRs for home use to practical use, longer recording time, smaller cassette size and higher reproduced image and sound quality than those of current AVCRs for home use are demanded. Therefore, known D1-format DVCRs for home use have drawbacks (1) and (2).
(1) Since the tape has excessively large additional areas which are not used for recording data, its recording time becomes short.
(2) Since the tape has too many linear tracks for editing, it is impossible to reduce the width of the tape.
Thus, in the known D1-format DVCRs for home use, there has been a keen demand for securing permissible reproduction quality for editing through elimination of the above mentioned drawbacks.